This invention relates to optical multiplexing systems and methods.
A system including several optical sensors or other devices can be multiplexed by time division multiplexing in which the path lengths between a source of optical radiation and a detector via each sensor are arranged to be different. In this way, a single short pulse of radiation injected by the source into the system, will result in a series of pulses at the detector spaced from each other in time by an amount according to the difference in path lengths via each sensor. The particular sensor associated with each return pulse can be identified by its location in the series of return pulses so that the outputs of the different sensors can be distinguished from one another.
One difficulty with this arrangement is that of ensuring that the pulses do not overlap at the output. To ensure that the output pulses associated with the same input pulse do not overlap, the input pulses must be made sufficiently short and the difference in the time delays between each sensor must be sufficiently long. In order to ensure that the earlier output pulses produced with one input pulse do not overlap with the later output pulses produced by a preceding input pulse, the input pulse repetition rate must be kept low. The maximum pulse repetition rate will be inversely proportional to the number of sensors. The shortening of the input pulses and the limitation on repetition rate has a severe effect on the power budget of the system and, therefore, on the signal-to-noise ratio at the detector.